Hard disks have always had sectors of 512 bytes, which means data is stored in 512 byte segments. For this reason operating systems work with 512 byte data packets.
Hard disks contain contain physical sectors of 512 bytes each. The increasing data density of hard disk in recent years has caused these 512 byte sectors to become increasingly smaller. Manufacturers noticed that the surface area could be used more efficiently with larger sectors. The reliability can also improve when ECC error correction can use sectors larger than 512 bytes. Another reason companies started working of larger sectors was that more recent operating systems also work with clusters larger than 512 bytes.
The consortium of hard disk manufacturers and related companies called IDEMA (International Disk Drive Equipment and Materials Association) assembled all parties in the year 2000 to address the issue. In 2010 a new standard for hard disks with 4k sectors was officially introduced. By now many hard disks feature 4k sectors, also called Advanced Format, especially disks 2 TB and larger.
4k sectors make it possible for manufacturers to use the surface area of hard disks in a more efficient manner. You can see below why, as sectors of 4096 bytes use much less overhead than the 512 byte ones. Reportedly the increase in efficiency is between 7 and 11 percent. Not only that, the reliability also increases since the ECC information is calculated over more data.
Conventional hard disks are transitioning to 4k sectors, but SSDs are storing data in 4k segment sins the beginning. SSDs consist of pages of 4 kB which is the small amount of data an SSD can read or write simultaneously. 4k makes sense here, as the file systems of recent OS (NTFS for Windows, HFS+ for Mac OS, ext3/4 for Linux, etc.) all work with 4 kB clusters. Newer generation SSDs even use 8k or 16k pages.
Hard disks with 4k sectors make more efficient use of the available space